Current understanding of the pulmonary circulation derives, essentially, from assumptions about the system that exclude realization of certain, subtle design features that have profound impact. Usual assumptions include linearity and time invariant parameters. Our recent work, however, indicates that blood flow control, pulmonary vascular properties and function, and cardiac-pulmonary interaction (with both ventricles) are associated with nonlinear or time variant behavior that provides passive and possibly even fluidic control. A more complete understanding offers potential for applications that have, heretofore, been largely unsuccessful. We propose to a) complete evaluation of nonlinear dynamic aspects of the major pulmonary vessels with respect to all velocities and stresses in the fluid and walls throughout the cardiac cycle for different states of the system. b) Evaluate and adjust present understanding of structure and function of the major vessels and of existing pulmonary models. c) Develop relations governing blood distribution in the lung during altered states. d) Investigate an approach to gauge pulmonary pressure noninvasively and to measure flow and pressure with the minimal incursion of only a pressure catheter. e) Establish relations of natural pulmonary vessel design as criteria for prosthetic vessel design to permit optimal flow characteristics with materials having desirable surface properties but inadequate material properties. Methods utilize theory supported by in-vitro, hydrodynamically similar, flow models and by animal experiments. Techniques will avoid compromise of normal function and bias (e.g. flow cuffs seriously compromise pulmonary trunk behavior). New concepts for nonlinear analysis has been developed during the present grant period as were physical models and techniques for in-vitro work. Relations to include branching phenomena and pulse propagation have commenced development. Noninvasive evaluations will utilize estimation techniques as a problem of signature analysis in conjunction with established pulmonary phenomena and invasive measurements. The flow-from-pressure measurement is via a development unique to our laboratory.